This proposal combines the development of polygenic models of evolution in heterogeneous environments with an empirical test of their validity in experimental populations. The implementation of a natural selection experiment in the laboratory is an important first step in the long term goal of applying these concepts to field populations. One-locus genetic models of variable environments (e.g. Levene's (1953) multiple-niche model), and the experiments they have inspired, have focused on the maintenance of genetic variation. However, these models cannot be directly applied to quantitative characters because the effects of allelic changes at single loci cannot generally be determined. In addition, the multiple-niche models describe only genotypic fitnesses; the effects of environmental modification of the phenotype, a common feature of polygenic traits, cannot be understood in a one-locus context. The only previous polygenic model (Slatkin, 1978) concerns a special case in which genotypes do not vary in the susceptibility to environmental modification, that is, when there is no genotype-environment interaction. The models described here use the idea that genotype-environment interaction can be expressed as a genetic correlation between the phenotype in two niches to illustrate that cross-environment genetic correlations can dramatically affect evolutionary trajectories and rates of approach to equilibrium. In most cases, the optimum phenotype in each environment is eventually attained; these models thus suggest an evolutionary mechanism for the norm of reaction (Schmalhausen, 1949). I propose here to test whether the predictions made by these models for the dynamics of evolution under hard and soft selection in different environments can be observed in experimental populations. The flour beetle, Tribolium will be exposed to two flour types in both constant and variable regimes. Genetic parameters and the intensities of selection will be estimated in the base population on 8 characters. These estimates will be used in the models to generate short-term predictions of evolutionary rates and trajectories in the variable environments for comparison to the observed course of evolution. Periodic re-estimation of the genetic parameters will be made by sib analysis to test the assumption that they remain constant. Several refinements of the models are outlined, including an agricultural application to the evolution of pest insects exposed to an array of resistant crop varieties. Such models have implications for pest control.